High capacity stacked DRAM device and process for making a smaller geometry

ABSTRACT

A DRAM having a theoretical cell layout efficiency of 100% and a density of up to four gigabits DRAM is obtained without sacrificing the storage capacitor values. This accomplishment is achieved by introducing landing pads in layout and obtaining narrow widths down to 1000A and small spaces down to 700 Å. The DRAM has active isolations, word lines, cup-shaped vertical capacitor walls, and bit lines. The process for forming small dimensions having this narrow width, narrow wall and the small space in ranges down 800 Å comprises depositing a form material on the surface of a product material. A portion of the form material is removed by RIE etching by using the lithography technique. A layer of masking material is deposited over the form material and product material, the layer of masking material having a thickness correlating to said desired width of product material. Masking material is removed by vertical RIE until the form material is exposed, leaving a predetermined width of masking material. Portions of the product material which are not protected by the masking material are removed to leave a desired width of product material corresponding to the width of the masking material. The corresponding process can be used to form spacings of corresponding dimensions.

This is a continuation of application Ser. No. 80/609,846, filed Mar. 1,1996, now U.S. Pat. No.5,946,566.

FIELD OF THE INVENTION

This invention relates to an high capacity DRAM device having a smallercell size as well as having a higher storage capacity. This process alsorelates to a process for preparing “memories” and other semiconductordevices with smaller dimensions and precise controls. In particular,this invention relates to a process for preparing DRAM's having asmaller cell size with high storage capacities and the cell layout of ahigh density DRAM product having a capacity as high as four gigabits.

BACKGROUND OF THE INVENTION

In recent years, in the area of semiconductor memory devices such asDRAM, 4M and 16M DRAMs have been mass-produced, and 64M DRAMs have beenstudied. In DRAMs, the typical three dimensional structures such as atrench type and a stack type have been developed. The trench type ismanufactured in a groove provided on the semiconductor substrate, andthe stack type is formed by laminating in three dimensions theconductive layers on the surface of the semiconductor substrate. Thetrench type has a flatter surface than the stack type, providingadvantages for lithography but has serious operating disadvantages. Theoperation voltage is changed by leakage of current and punch-throughbetween adjacent trenches. Electron-hole pairs generated by α-particlestransmitted inside the substrate are also a problem.

The stack type is formed by laminating element layers on the substrate,and the fabrication process sequence is simpler than for the trench typeand does not have the operating deficits noted above. As a result, thestack type is more attractive than the trench type.

A limiting factor in the construction of stack type DRAMs in smallercell sizes is the minimum storage capacity of 25 fF required for properoperation of a DRAM, that is, the cell capacity required per cell andthe practical limit of photolithography techniques for achieving smallerdimensions. As the memory device is made to be more highly integratedand thus smaller in size, the area occupied by each cell is reduced,thus reducing the area available for each capacitor. To be functionallyoperable, the capacitor must have a large capacity, even as the size ofthe memory cell is reduced.

The chip size of a DRAM product is determined by the formula:

Chip Area=AP+AM

Where:

AP is the Area of Peripheral circuits; and

AM is the Area of total Memory cells and is calculated by the formula:

AM=Total Bits (or density)×a Cell Area

Normally, AM occupies more than 55 percent of the total chip area in ahigh density DRAM. Because the smaller the chip size, the lower theproduction cost, every effort is directed to reducing the cell size. Itcan be shown that the memory cell size can be estimated by the formula:

Cell Area=2×(AP+2δ)×WP/AE

 Wherein:

AP=Active Pitch;

δ=Spacing of a bit line contact to the word line due to alignmentlimitations of photolithography (alignment errors);

WP=Word Line Pitch; and

AE=Area Efficiency.

In the produce and process of this invention, AE can be greater thanpreviously known configurations, being above 80% and as high as about100%.

Prior art approaches have focused on reducing the Cell Area by scalingbut have reached limits in size reduction and tolerances due to thelimits of photolithography, process techniques, and the need to make acapacitors having capacities greater than 25 fF. Similar constraintshave limited the Area Efficiency for a typical 16 M DRAM to less than 80percent.

OBJECTS AND SUMMARY OF THE INVENTION

It is an object of the present invention to provide a process formanufacturing a semiconductor device which provides component widths andspacings of in a range down to 1000 Å and smaller in horizontal planesby using the existing optical stepper or other advanced conventionallithographic exposure systems and even smaller dimensions in a rangedown to 700 Å using more advanced X-ray and more precise RIE techniques.

It is another object of this invention to provide a smaller DRAM cellstructure which provides a theoretical efficiency of 100 percent.

It is a still further object of this invention to enable theconstruction of DRAMs having a density of up to four gigabits per devicewithout sacrificing the cell capacity.

A further object of this invention is the provision of a DRAM havingcomponents which are entirely constructed in straight line structures,avoiding stress points, and yielding a more stable, low leakage product.

It is a still further object of this invention to provide a DRAM havingword and active line arrays each of which are straight, have a uniformwidth, and have a uniform, minimum spacing from adjacent members oftheir respective arrays, the word and bit lines being in a configurationperpendicular to each other. In summary, one process of this inventionis to produce a desired width of a product material in small dimensionsin a range down to 800 Å. The process comprises the following steps:

a) depositing a form material on the surface of a product material;

b) removing a portion of the form material by vertical etching usingphotolithography to leave a sidewall of said form material;

c) depositing a layer of masking material over the form material andproduct material, the layer of masking material having a thicknesscorrelating to said desired width of product material;

d) removing masking material by vertical RIE until the form material isexposed, leaving a predetermined width of masking material, and removingthe form material until the underlying product material is exposed;

e) removing portions of the product material which are not protected bythe masking material to leave a desired width of product materialcorresponding to the width of the masking material; and

f) removing the masking material, leaving a desired width of saidproduct material.

The form material can be nitride, the masking material can be oxide, andthe product material is a conductor such as doped polysilicon. Examplesof suitable products formed by this process are word lines and capacitorplates.

Another process of this invention forms a small spacing d between widthsof material. This can be useful for reducing spacings between capacitorplates, conductors or transistors, and in reducing the size of fieldoxide areas, for example. It can also yield products such as bit linesor word lines with reduced widths. The process for forming a desiredspace between adjacent portions of a product material having a width ecomprises the following steps:

a) depositing a form material on the surface of a product material;

b) removing a center portion of the form material by vertical etchingusing photolithography to leave form materials having widths W withopposed sidewalls spaced apart by a distance D which is greater than thedesired spacing d by 2Δ;

c) depositing a layer of masking material over the form material andproduct material, the layer of masking material having a thicknesscorrelating to Δ;

d) removing masking material by vertical RIE until the form material isexposed, leaving Δ widths of masking material contacting each of theopposed sidewalls of the form material;

e) removing form material by etching;

e) removing portions of the product material which are not protected bythe masking material; and

f) removing the form material and the masking material, leaving adjacentpairs of adjacent widths of product material, each having a width e ofin a range down to 800 Å, the desired spacing d between adjacent pairsof product material being in a range down to 700 Å; and a spacing Wbetween adjacent widths of a product material.

In this process, each of the form material, masking material and productmaterial is a member independently selected from the group consisting ofnitride, oxide, conductor and laminate combinations thereof. Preferably,the form material and the masking material are not the same member, andthe masking material and the product material are not the same member.For example, the form material include nitride, oxide, or combinationsthereof; the masking material can be oxide; and the product material canbe doped polysilicon or metal.

In one embodiment, the form material is nitride, the masking material isoxide, and the product material is a conductor. The product material candoped polysilicon.

The adjacent widths of product material can be word lines capacitorplates, for example.

Another embodiment of the process of this invention forms a desiredspacing d in small dimensions in a range down to 700 Å between adjacentwidths of a product material. It comprises the following steps:

a) depositing a form material on the surface of a product material;

b) forming an array of photolithographic masking materials spaced apartby a distance D;

c) removing portions of the form material by vertical etching to leavean array of form materials with opposed sidewalls spaced apart by adistance D which is greater than spacing d by 2Δ and removing thephotolithographic masking materials;

c) depositing a layer of second masking material over the form materialand product material, the layer of second masking material having athickness correlating to Δ;

d) removing second masking material by vertical RIE until the formmaterial is exposed, leaving Δ widths of opposed second masking materialcontacting each of the opposed sidewalls of the form material, thedistance between the opposed widths of second masking material being ina range in a range down to 700 Å.

In one embodiment of this process, the form material, masking materialand product material are each individually selected from the groupconsisting of nitride, oxide, conductor and laminate combinationsthereof. Preferably, the form material and the masking material are notthe same member and the masking material and the product material arenot the same member.

In another embodiment of the process, the form material, maskingmaterial and product material are each individually selected from thegroup consisting of nitride, oxide, conductor and laminate combinationsthereof, but the form material and the masking material are not the samemember.

The process can be followed by the step of removing portions of theproduct material which are not protected by the masking material by RIE,and optionally, all or only part of the product material not protectedby the masking material can be removed.

The process can be followed by an alternative steps of removing theproduct material by RIE, and removing the form material and the maskingmaterial by etching, leaving the product material widths separated bythe desired space d.

In one embodiment, the product material is a layer of nitride supportedby a silicon substrate and the masking material is polysilicon.

The process can be followed by the following additional steps:

oxidizing the exposed surfaces to effect oxidation of the polysiliconand the underlying substrate silicon; and

removing the form material and polysilicon to leave a silicon substratehaving field oxide portions with widths in a range down to 1000 Å.

The products of this invention includes memory having a plurality oflinear straight word lines which have a uniform relative spacing andwidth; a plurality of active spaces which are linear, straight and havea uniform width and spacing; and combinations thereof. The product canbe a stacked capacitor DRAM device.

Another memory device of this invention has a plurality of linearstraight bit lines; a plurality of linear straight word lines which havea uniform relative spacing and width; a plurality of active spaces whichare linear, straight and have a uniform width and spacing, or anycombinations of any two or three thereof. The products can be a stackedcapacitor DRAM device.

Another memory device of this invention has active area contacts whichare isolated from adjacent active area contacts by non-conductinglayers, the active area contacts having small widths of in a range downto 700 Å. A conductive landing pad layer contacts each of the activearea contacts and overlaps a portion of the adjacent non-conductinglayer, thereby enlarging the effective surface area of each areacontact. Such a memory device can also include a parallel array of wordlines extending in a direction, wherein the active area contact is a bitline contact, and the landing pad extends from the active area to aposition displaced therefrom in said direction. Such a device can astacked capacitor DRAM device.

Another process of this invention forms a cup-shaped capacitor plate fora stacked capacitor memory device. The process comprises the followingsteps:

a) depositing a conductive layer in electrical contact with an activecapacitor contact area of a substrate;

b) depositing a upper layer of nitride, oxide or combination thereof onthe surface of the conductive layer;

c) forming a mask on the surface of the upper layer, the outer boundaryof the mask positioned to define the inner walls of the capacitor;

d) removing the upper layer and optional portions of the conductivelayer by RIE to a depth which correlates to the sidewall thickness ofthe capacitor and removing the mask;

e) depositing a layer of oxide material on the surface obtained in step(d);

f) removing oxide by RIE until oxide is removed from the upper layer,leaving a shoulder of mask oxide on the surface of the upper layer andthe conductive layer;

g) removing the upper layer by etching and removing portions of theconductive layer which are not covered by the shoulder of mask oxide byRIE, leaving the sidewalls and floor of the capacitor;

h) removing mask oxide by etching to leave a cup-shaped capacitor plate;

I) depositing a layer of dielectric on the surface of the capacitorplate; and

j) forming a conductive layer on the layer of dielectric to form acapacitor.

In this process, a portion of the conductive layer can be supported on alayer of support oxide, and step (h) can comprise comprises mask oxideand support oxide by etching to leave a cup-shaped capacitor plate, atleast a portion of the underside of the floor thereof being availablefor capacitor surface. In this process, the width of the shoulder ofmask oxide can be in a range down to 700 Å, for example.

A still further process of this invention is an array of transistors. Itcomprises the following steps

a) depositing a layer of gate material on a layer of gate oxidesupported by active silicon substrate;

b) depositing an upper layer comprising nitride or oxide or combinationsthereof on the gate material;

c) forming an array of photolithography masked areas defining spacesbetween adjacent transistor gates on the upper layer, the distancesbetween adjacent masked areas is D;

d) removing the upper layer not covered by the masking areas by RIE andremoving the photoresist;

e) depositing mask oxide on the upper surface obtained in step (d);

f) removing mask oxide by RIE, leaving shoulders of oxide mask adjacentthe upper layer having a thickness Δ;

g) removing upper layer by etching and removing gate material by RIE toleave an array of mask oxide protected gates;

h) removing mask oxide by etching, leaving an array of gates with widthe.

In this process, the silicon substrate between adjacent gates formed instep (g) can be weakly doped by ion implantation and can be followed bythe following additional steps:

i) a layer of masking oxide is deposited on the product of step (h);

j) masking oxide is removed by RIE to leave shoulders of mask oxideadjacent the gates and exposed areas of active substrate between theshoulders; and

k) exposed areas of active substrate are doped by ion implantation.

A still further process of this invention smaller, precise field oxidein a semiconductor device. It comprises the following steps:

a) depositing successive pad oxide, polysilicon and upper nitride layerson a silicon substrate;

b) forming resist mask portions on the nitride layer by photolithographyto define the field oxide area and portions of the nitride to remain andremoving the areas of nitride and a partial polysilicon unprotected bythe mask portions by RIE, and removing the resist mask portions;

c) depositing a masking layer of polysilicon on the upper surfaces ofthe product of step (b);

d) removing the masking polysilicon by RIE to leave shoulders of maskpolysilicon and exposed areas of nitride between the shoulders;

e) exposing the product of step (d) to oxidation to grow field oxide inthe exposed areas of pad oxide.

Other features and advantages of the invention will be apparent from thefollowing description taken in connection with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional representation of an intermediatein the process after the formation of the word line gates.

FIG. 1A is a top view of the representation in FIG. 1, showing therelative shapes and positions of the superimposed layers.

FIG. 2 is a schematic cross-sectional view of the product in FIG. 1after deposition of a layer of oxide.

FIG. 3 is a schematic cross-sectional view of the product in FIG. 2after RIE to expose the channels and ion implantation of the channels.

FIG. 4 is a schematic cross-sectional representation of the product inFIG. 3 after deposition of a layer of oxide.

FIG. 5 is a schematic cross-sectional representation of the product ofFIG. 4 after RIE to expose the landing pad contact areas.

FIG. 6 is a schematic cross-sectional representation of the product ofFIG. 4 after formation of the conductive landing pads on the channels.

FIG. 6A is a top view of the representation in FIG. 6, showing therelative shapes and positions of the superimposed layers, including thelanding pads.

FIG. 7 is a cross-sectional representation of a further intermediate inthe process of this invention after formation of the bit line.

FIG. 7A is top view of the product after exposing the bit line contact,showing the relative shapes and positions of the superimposed layers.

FIG. 7B is an enlarged schematic view of the bit line structure shown inFIG. 7.

FIG. 7C is a top view of the product after formation of the bit line,showing the relative shapes and positions of the superimposed layers.

FIG. 8 is a cross-sectional representation of a further intermediate inthe process of this invention after forming the storage contact andforming the polysilicon layer from which the capacitors are to beformed.

FIG. 8A is a top view showing the relative shapes and positions of thesuperimposed layers after formation of the holes to the storagecapacitor landing pads.

FIG. 9 is a schematic cross-sectional representation of a portion of therepresentation in FIG. 8 from which the storage capacitor is to beformed.

FIG. 10 is a schematic cross-sectional representation of theintermediate shown in FIG. 9 after the center form has been shaped byconventional photolithography procedures.

FIG. 11 is a schematic cross-sectional representation of theintermediate shown in FIG. 10, after formation of the oxide mask.

FIG. 11A is a schematic representation showing the dimensionalrelationship between the thickness of the mask forming material depositand the width of the mask formed in the process of this invention.

FIG. 11B is a schematic representation of the system of this inventionfor forming small widths of material.

FIG. 12 is a schematic cross-sectional representation of theintermediate shown in FIG. 11 after removal of a portion of thepolysilicon layer by vertical RIE.

FIG. 13 is a schematic cross-sectional representation of theintermediate shown in FIG. 12 after deposition of the dielectricmaterial and the conductive material from which the capacitor plate isto be formed.

FIG. 14 is a schematic cross-sectional representation of the completedDRAM cell following the capacitor formation.

FIG. 14A is a top view showing the relative shapes and positions of thelayers in the final device.

FIGS. 15-24 are schematic representations of the process of thisinvention for preparing word gate structures which have smaller widthsand spacings and for preparing small spacings in a range down to 700 Å.

FIGS. 25-34 are schematic representations of the process of thisinvention for preparing small spacings in a range down to 700 Å andwhich can yield smaller, precision field oxide areas.

DETAILED DESCRIPTION OF THE INVENTION

Certain terms used herein are abbreviated terms in the art. Unlessotherwise specified, “oxide” means silicon dioxide; “nitride” meanssilicon nitride; polysilicon means polycrystalline or amorphous silicon;“BOE” means buffered oxide etching solution (containing ammoniumfluoride and hydrofluoric acid; “RIE” means conventional verticalreactive ion etching process or anisotropic plasma etching; “polycide”means a composite of polysilicon and a refractory metal such asmolybdenum, platinum, silicide, titanium silicide or tungsten silicide,for example; “conductor” means a conductive material which can be dopedpolysilicon, polycide, refractory or non-refractory metal and the like;and “HTO” means CVD deposited silicon dioxide at high temperatures.

FIG. 1 is a schematic cross-sectional representation of an intermediatein the process after the formation of the word line gates. FIG. 1A is atop view of the representation in FIG. 1, showing the relative shapesand positions of the superimposed layers. These early steps areconventional procedures, known in the art, portions of which aredescribed in U.S. Pat. No. 5,114,873, for example, the entire contentsof which are hereby incorporated by reference. This intermediate isprepared by the following steps. An N or P type semiconductor substrate2 is weakly doped with either a P type impurity such as boron or an Ntype impurity such as phosphorus, arsenic or antimony to form thecorresponding P-well or N-well 4. In the process described hereinafter,an P-well is formed by weakly doping the substrate with boron in P typesemiconductor substrate for purposes of illustration and example, not byway of limitation.

A pad oxide layer is grown on the surface of a silicon substrate andcovered with a layer 0 Å to 1000 Å of polysilicon, and a layer ofnitride is deposited thereon. Using conventional lithography, a mask ofphotoresist material is deposited on the surface, developed, the nitridelayer is removed from the field oxide region, and the photoresist isremoved. The field oxide regions 6 are then grown to isolate the cell.The nitride, polysilicon and oxide are then removed to expose thesilicon channel. The channel is doped using conventional ionimplantation with a conventional photolithography mask.

A layer of gate oxide 8 having a thickness of from 40 Å to 200 Å isgrown on the surface, and a layer of gate material 10 is depositedthereon. Suitable gate materials are doped polysilicon, polycide orcombinations thereof. On this surface, a layer 12 of 0 Å to 2500 Å ofoxide is deposited. Using conventional lithographic techniques, theexposed oxide layer is removed by RIE. The exposed polysilicon isremoved by RIE etching, leaving the word line conductive gate layers 10.The exposed N− channels are subjected to light ion implantation with N−dopants such as phosphorous, arsenic or antimony, for example, and theP− channels are subjected to light ion implantation with P− dopant,boron or boron difluoride.

FIG. 2 is a schematic cross-sectional view of the product in FIG. 1after deposition of a 1000 Å to 1500 Å layer of oxide 18 on the surface.

FIG. 3 is a schematic cross-sectional view of the product in FIG. 2after ion implantation by the following process. N+ channels aresubjected by ion implantation with N+ dopants, phosphorous, arsenic orantimony, for example, and the P+ channels are subjected to P+ dopantimplantation with boron or boron difluoride, for example. The oxidespacers 20 prevent encroachment of the implanted areas 22 on thesubstrate underlying the word lines and leave N− doping areas 24.

FIG. 4 is a schematic cross-sectional representation of the product inFIG. 3 after deposition of a layer of oxide 26.

FIG. 5 is a schematic cross-sectional representation of the product ofFIG. 4 after removal of the oxide covering the landing pad contactsareas 14 and 16 by conventional photolithography and RIE.

FIG. 6 is a cross-sectional representation of a further intermediate inthe process of this invention after formation of the landing pads 28 and30 according to the following process. Referring to FIG. 6, a layer offrom 1000 Å to 2500 Å of polysilicon is deposited over the surface, andthe polysilicon can be doped during or after deposition. Usingconventional photolithography techniques, portions which are not coveredby photoresist are removed by etching to leave separated polysiliconcapacitor landing pads 28 and bit line landing pad 30. FIG. 6A is a topview of the representation in FIG. 6, showing the relative shapes andpositions of the superimposed layers.

FIG. 7 is a cross-sectional representation of a further intermediate inthe process of this invention after formation of the bit line 32according to the following procedure. Referring to FIG. 7, a 1000 Å to3500 Å layer of oxide 34 is deposited over the entire surface obtainedin FIG. 6. Using conventional photolithography, a portion of the oxidelayer covering the bit line landing pad 16 is removed by RIE to form abit line contact 31. FIG. 7A is top view of the product after exposingthe bit line contact, showing the relative shapes and positions of thesuperimposed layers. A conductive material such as doped polysilicon,polycide or metal is deposited on the surface and etched by conventionalphotolithography to leave a bit line 32 on extension of the bit linelanding pad 30. FIG. 7B is an enlarged schematic view of the bit linestructure shown in FIG. 7 showing the overlap of the bit line 32 withthe edges of the oxide layer 34. FIG. 7C is a top view of the productafter formation of the bit line, showing the relative shapes andpositions of the superimposed layers.

FIG. 8 is a cross-sectional representation of a further intermediateafter formation of the polysilicon layer from which the capacitors areto be formed by the following process. Referring to FIG. 8, sequentiallayers are formed comprising a lower layer of about 1500 Å to 4000 Å ofoxide 36, an intermediate layer of 100 Å to 500 Å of nitride 38, and anupper layer of 500 Å to 3000 Å of oxide 40 are deposited over thesurface obtained in FIG. 7, isolating the bit line 32. Usingconventional photolithography techniques, capacitor contact holes 42 areetched through the sequential layers to uncover the storage capacitorlanding pads 28. A thick layer (3000 Å to 10,000 Å) of polysilicon 44 isthen deposited over the entire surface and in the holes 40. Thepolysilicon can be doped during or after deposition. FIG. 8A is a topview showing the relative shapes and positions of the superimposedlayers after formation of the holes to the storage capacitor landingpads.

FIGS. 9-13 are schematic cross-sectional representations showing stepsin the process of this invention for preparing high precision, maximumsurface area storage capacitors.

FIG. 9 is a schematic cross-sectional representation of a portion of therepresentation in FIG. 8 including the hole 42, layers 36, 38, 40 andpolysilicon layer 44, the polysilicon layer 44 being in electricalcontact with the landing pad 28. An optional thin oxide layer 46 (0 Å to200 Å) and a nitride layer 48 (1000 Å to 3000 Å) are deposited on thesurface of polysilicon layer 44.

FIG. 10 is a schematic cross-sectional representation of theintermediate shown in FIG. 9 after the center form has been shaped bythe following conventional photolithography procedures. Using a mask ofphotoresist material, the exposed areas of the nitride layer 48 and theoxide layer 46 are removed by conventional etching. An upper portion ofthe polysilicon layer 44 is optionally removed by RIE to form a sidewall50 and optional shoulder 52 having a height “a” representing a reductionof polysilicon of 0 Å to 3000 Å. The photoresist is then removed.

FIG. 11 is a schematic cross-sectional representation of theintermediate shown in FIG. 10, after formation of the oxide mask. Thismask is formed by the following process. A layer of CVD oxide isdeposited on the entire surface. This invention is based on thediscovery that of a new procedure for increasing the precision ofspacing and width in the horizontal plane and floor thickness, aprocedure which is far more precise and yields far closer tolerancesthan the photolithography based procedures. The thickness of depositedlayers can be controlled with high precision to uniform depositthickness in a range down to 200 Å. We have discovered a procedure whichtranslates the high precision coating thickness to equally precisehorizontal widths or spaces.

Referring to FIG. 11A, when an oxide layer of thickness “t” is depositedon a surface, and the surface is etched by RIE, a shoulder 54 of oxideis formed. The width of the shoulder “t′” is a function the thickness t,is proportional to the thickness t and is approximately equal to 0.8 t.By controlling the thickness to a precise desired value, the shoulderwidth t′ can be controlled to the same value and precision, an oxidecoating thickness of 1000 Å to 2000 Å yielding a corresponding 800 Å to1600 Å width in the shoulder 54 in FIG. 11. The shoulder 54 in FIG. 11can then be used as a precision mask for etching. This formula fits thetypical case where t is smaller than t′, and it may not fit other caseswhere the RIE process is abbreviated or extended beyond the illustratedstage of etching and shoulder formation.

FIG. 11B is a schematic representation of the system of this inventionfor forming small widths of material. The product material A can bemetal, oxide, polysilicon, nitride or other selected material. B, theform material and C, the mask material each can be metal, oxide,polysilicon, nitride or other selected material so long as A and B aredifferent and B and C are different, that is, have etching differentialswhich can provide the relative component functions during RIE oretching.

FIG. 12 is a schematic cross-sectional representation of theintermediate shown in FIG. 11 after removal the outer portion of thepolysilicon layer 44 by the following process. The nitride layer 48 andoxide layer 46 are removed by conventional wet or dry etching processes.Then, the exposed polysilicon is time etched by RIE, leaving theintegral box or cup-shaped capacitor wall structure 56 and floor 58. Thewidth of the walls 56 can be any selected width in a range down to about700 Å, obtained by selecting an oxide thickness t which has thecorresponding proportional thickness. Since the shoulder 52 is lowerthan the upper surface of the polysilicon layer 44, the shoulder portion52 is removed before all of the central polysilicon, leaving a thinfloor layer 58 remaining when the etch has reached the upper surface ofthe oxide layer 40. Alternatively, by increasing the RIE etching timie,the floor layer can be completely removed, if desired for a specificapplication.

It will be obvious to a person skilled in the art that by substitutingother materials having contrasting etching resistance'ss and selectionof respective etching solutions and gases, the polysilicon can bereplaced by other conductors or semiconductors to yield a wall of saidmaterial. Alternatively, the materials could be reversed to yield a wallof a contrasting materials such as silicon dioxide, for example.

FIG. 13 is a schematic cross-sectional representation of theintermediate shown in FIG. 12 after formation of the second capacitorplate by the following procedure. The oxide layer 40 and oxide mask 54are removed by exposure of the surface to buffered oxide etch solution(BOE, HF and NH₄F), leaving the fully formed capacitor plate 60 withexposed upper and lower surfaces, the edges 62 remaining in a sharp,defined and non-eroded condition.

A thin dielectric insulating layer such as nitride, titanium oxide,oxide, or combination thereof is deposited on all exposed surfaces ofplate 60. If nitride is used, any pinholes are closed by conventionaloxide growth. The capacitor plate 60 with the dielectric insulatinglayer is then covered with from 1000 Å to 3500 Å of a conductor 64 suchas doped polysilicon, polycide, metal or combinations thereof to form acomplete capacitor.

FIG. 14 is a schematic cross-sectional representation of the devicefollowing the capacitor formation. The entire side surfaces, upper andlower surfaces of the plate 60 are available as plate surfaces,providing sufficient capacitance per plate for size reductions down tosub-micron scales. Capacitance can be further increased by increasingthe height “h” to any desired figure, permitting cell sizes or areas aslow as 0.2μ² per cell. The width of the capacitor plate sidewall “e” canbe in a range down to as low as 800 Å, and the spacings between adjacentcapacitors “c′” can be as low as 1000 Å, permitting use of substantiallyall of the cell width as capacitor width.

Referring to FIGS. 12-14, the storage spacing distance c′ is alsodetermined by the essential steps of the process described with respectto FIGS. 15-22. The oxide shoulders 54 (FIGS. 11-12) for adjacentcapacitor plates 60 (FIG. 13) determine the spacing between adjacentstorage cell surfaces. The application of the process of this inventionto obtain spacings d with sizes in a range down to 700 Å is described ingreater detail with respect to FIGS. 15-22 hereinafter.

FIG. 14A is a top view showing the relative shapes and positions of thelayers in the final device.

Referring to FIGS. 7B and 8A, the configuration for the device of thisinvention includes an array of primary bit lines 32 and an array of wordlines 10, the primary bit lines 32 being oriented perpendicular to theword lines 10, and a landing pad 30 extending from each cell to acontact 31 for bit line 32 laterally displaced from the center of thecell. The entire upper surface of the cell is available for thecapacitor. Together with the smaller capacitor cell walls and distancesbetween adjacent cells, this configuration has a theoretical areaefficiency of 100 percent, making available a product having apreviously unattainable number of cells per chip. DRAMs of thisconstruction have a density of greater than 1 megabit and can be up tofour gigabits.

It will be readily apparent to a person skilled in the art that thenovel process techniques of this invention can be applied to reduce thecell size, and in return, reduce the chip size and increase the areaefficiency of other semiconductor devices such as SRAM, ROM, FlashE²PROM, and N-channel or P-channel FET devices.

FIG. 15 is a schematic cross-sectional representation of an initialmultilayer structure comprising silicon substrate layer 70; thin gateoxide layer 72; conductive word line material 74 such as dopedpolysilicon, a refractory metal such as tungsten, polycide orcombinations thereof; nitride, oxide or combinations thereof 76; andphotoresist mask portions 78, all prepared by conventional procedures.

FIG. 16 is a schematic cross-sectional representation of the product ofFIG. 15 following removal of exposed nitride or oxide 76, andoptionally, a portion of the word line material 74 by conventionalvertical RIE procedures, leaving optional shoulder 80.

FIG. 17 is a schematic cross-sectional representation of the product ofFIG. 16 following removal of the mask portions 78 by conventionalprocedures, leaving the nitride 76 and critical side walls 82 forformation of an oxide word line mask.

FIG. 18 is a schematic cross-sectional representation of the product ofFIG. 17 following deposit of mask oxide layer 84 in a thickness whichcorresponds to the desired width of the word line, using the principalsand relationship described above with respect to FIG. 11A.

FIG. 19 is a schematic cross-sectional representation of the product ofFIG. 18 following removal of the layer by RIE, leaving the oxide masks86.

FIG. 19A is a schematic representation showing the intermediate processof this invention for preparing small spaces in product materials afterforming the shoulder having width A as shown in FIG. 11A, productmaterial is etched, and the nitride and mask layer is removed. A′ can beany desired product material such as a metal, oxide, polysilicon,nitride or the like. B′, the form material and C′, the masking materialcan be metal, oxide, polysilicon, nitride or the like, and contrary tothe small width relationships described above with respect to FIG. 11B,the form materials B′ and mask materials C′ can be the same since theydo not require differential etching rates.

FIG. 20 is a schematic cross-sectional representation of the product ofFIG. 19 following removal of the nitride layer 76 by conventional wet ordry etching procedures.

FIG. 21 is a schematic cross-sectional representation of the product ofFIG. 20 following conventional vertical RIE of the exposed gate material74, forming the word lines 88.

FIG. 22 is a schematic cross-sectional representation of the product ofFIG. 21 following removal of the oxide masks 86 and exposed portions ofthe gate oxide layer 72 by conventional BOE processes. The product isthen processed according to the procedures described hereinabove tomanufacture the finished memory device.

FIGS. 23 and 24 are schematic cross-sectional representations of analternative product which can be prepared from the intermediate shown inFIG. 19. The representation in FIG. 23 is obtained following verticalRIE of the exposed product material 74 without removing the nitridelayer 76. The product in FIG. 24 is obtained after removal of thenitride and oxide by conventional etching processes.

Referring to FIG. 19, the desired spacing d between word lines 88 can berepresented by the equation:

d=D−2Δ

For example D can be as low as 0.4μ using advanced, conventionallithography such as the currently available optical steppers. Δ can beas 0.15μ or lower, determined by the thickness of layer 84 (FIG. 18)after forming the shoulder having width Δ as shown in FIG. 11A, gatematerial is etched, and the nitride and mask layer is removed. Theresulting d is 0.1μ or 1000 Å.

The process of this invention can also be used to grow precisely definedand smaller areas of field oxide.

FIG. 25 is a schematic representation of a section of a memory deviceformed by the following procedure. A layer of pad oxide 100 having athickness of 50 Å to 250 Å is deposited or grown on a silicon substrate102. A layer of polysilicon 104 having a thickness of from 0 Å to 1000 Åand a layer of nitride 106 having a thickness of 1000 Å to 2000 Å isdeposited on the pad oxide 100. A mask 108 is formed by conventionallithography.

FIG. 26 is a schematic representation of the component of FIG. 25following the removal of the nitride in the opening of the mask portions108 by conventional procedures.

FIG. 27 is a schematic representation of the component of FIG. 26following removal of portions of polysilicon 104 which are not protectedby the nitride portions 106 by RIE partially and removal of thephotoresist.

FIG. 28 is a schematic representation of the component of FIG. 27following deposition of a layer of polysilicon correlating to thedesired thickness of the shoulder 110 (FIG. 29) as described hereinabovewith respect to FIG. 11A.

FIG. 29 is a schematic representation of the component of FIG. 28following removal of polysilicon 108 by RIE until the surface of thenitride 106 is exposed, leaving the mask shoulders 110 between thenitride form material 106.

FIG. 30 is a schematic representation of the component of FIG. 28following removal of polysilicon 108 by RIE and optional removal of aportion of the polysilicon 104 by RIE to form a channel with a thinnedpolysilicon portion 112 at the bottom thereof.

FIG. 31 is a schematic representation of the component of FIG. 27 orFIG. 28 following oxidation of the polysilicon surfaces exposed in thechannel, the thinned bottom portion 112 and a portion of the underlyingsilicon 102 to form a silicon oxide 114.

FIG. 30 is a schematic representation of the component of FIG. 29following removal of all of the nitride 106 and any remainingpolysilicon, yielding a substrate 102 with spaced field oxide portions116.

FIGS. 33 and 34 are schematic cross-sectional representations of analternative product which can be prepared from the intermediate shown inFIG. 28. The representation in FIG. 33 is obtained following verticalRIE of the exposed masking material 108 and then polysilicon 104 untilthe pad oxide layer 100 is reached, without removal of the nitride 104.The product in FIG. 34 is obtained after removal of the nitride andoxide by conventional etching processes.

With the process of this invention, the spacings between the opposedshoulders 110 can be in a range down to 700 Å, yielding accurately sizedfield oxide portions 116 with widths which are in a size range of downto 1000 Å.

As described above with respect to the manufacture of the capacitorstructure, the process of this invention yields far smaller widths,spaces, simultaneously, with conventional lithographic, deposition andetching procedures than can be achieved by previously known processes.The spacings between word lines “d” and the widths “e” can be as smallas 700 Å or smaller, yielding memory devices with cell sizes as low as0.2μ² and lower.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

The invention claimed is:
 1. A process for forming a desired spacing dbetween adjacent widths of a product material, comprising: a) depositinga form material on the surface of a product material; b) formingpatterns of photolithographic masking materials spaced apart by adistance D; c) removing portions of the form material by etching toleave the patterns of form material with opposed sidewalls spaced apartby a distance D which is greater than spacing d by 2Δ and removing thephotolithographic masking materials; d) depositing a layer of secondmasking material over the form material and product material, the layerof second masking material having a thickness correlating to Δ; e)removing portions of the second masking material by etching until theform material is exposed, leaving Δ widths of opposed second maskingmaterial contacting each of the opposed sidewalls of the form material,the distance between the opposed widths of second masking material beingin a range down to 700 Å; f) removing portions of the form material andthe product material not protected by the second masking material; andg) removing the remaining portions of the second masking material,leaving the product material formed into multiple capacitive plates, andwherein at least two of the capacitive plates are separated by spacingd; wherein the form material, masking material and product material areeach individually selected from the group consisting of nitride, oxide,conductor and laminate combinations thereof, but the form material andthe masking material are not the same member and the masking materialand the product material are not the same member.
 2. A process of claim1 wherein the form material is nitride, the masking material is oxide,and the product material is a conductor.
 3. A process for forming adesired spacing d between adjacent widths of a product material,comprising: a) depositing a form material on the surface of a productmaterial; b) forming patterns of photolithographic masking materialsspaced apart by a distance D; c) removing portions of the form materialby etching to leave the patterns of form material with opposed sidewallsspaced apart by a distance D which is greater than spacing d by 2Δ andremoving the photolithographic masking materials; d) depositing a layerof second masking material over the form material and product material,the layer of second masking material having a thickness correlating toΔ; e) removing portions of the second masking material by etching untilthe form material is exposed, leaving Δ widths of opposed second maskingmaterial contacting each of the opposed sidewalls of the form material,the distance between the opposed widths of second masking material beingin a range down to 700 Å; f) removing portions of the form material andthe product material not protected by the second masking material; andg) removing the remaining portions of the second masking material,leaving the product material formed into multiple capacitive plates, andwherein at least two of the capacitive plates are separated by spacingd; wherein the form material, masking material and product material areeach individually selected from the group consisting of nitride, oxide,conductor and laminate combinations thereof, but the form material andthe masking material are not the same member.
 4. A process of claim 3wherein the form material is nitride, the masking material is oxide, andthe product material is a conductor.
 5. A process for forming a desiredspacing d between adjacent widths of a product material, comprising: a)depositing a form material on the surface of a product material; b)forming patterns of photolithographic masking materials spaced apart bya distance D; c) removing portions of the form material by etching toleave the patterns of form material with opposed sidewalls spaced apartby a distance D which is greater than spacing d by 2Δ and removing thephotolithographic masking materials; d) depositing a layer of secondmasking material over the form material and product material, the layerof second masking material having a thickness correlating to Δ; e)removing portions of the second masking material by etching until theform material is exposed, leaving Δ widths of opposed second maskingmaterial contacting each of the opposed sidewalls of the form material,the distance between the opposed widths of second masking material beingin a range down to 700 Å; f) removing portions of the form material andthe product material not protected by the second masking material; andg) removing the remaining portions of the second masking material,leaving the product material formed into multiple capacitive plates, andwherein at least two of the capacitive plates are separated by spacingd; wherein only a portion of the product material not protected by themasking material is removed.
 6. A process of claim 5 wherein the formmaterial is nitride, the masking material is oxide, and the productmaterial is a conductor.
 7. A process of claim 5 wherein the formmaterial is oxide, the masking material is oxide, and the productmaterial is a conductor.
 8. A process of claim 5 wherein all of theproduct material not protected by the masking material is removed.
 9. Aprocess of claim 5 including removing the form material and the maskingmaterial by etching.
 10. A method for forming multiple capacitor plateswith at least two of the capacitor plates separated by a distance whichis less than a minimum feature size, the method comprising: depositing afirst insulator on the surface of a conductor; forming a mask patterndisposed over the first insulator, wherein the first insulator isexposed through a window in the mask pattern; removing portions of thefirst insulator and the conductor to form an opening corresponding tothe window, wherein an amount of the removed conductor correlates to aplate thickness; depositing a second insulator over the first insulatorand the exposed conductor, wherein a thickness of the second insulatorcorrelates to a spacer width; removing portions of the second insulator,wherein portions of the conductor are exposed and portions of the secondinsulator form spacers on opposite walls of the opening, and wherein aseparation distance between the spacers is less than a feature size; andremoving portions of the first insulator and the conductor which are notprotected by the spacers, wherein the conductor is formed into a firstcapacitive plate of the plate thickness and a second capacitive plate ofthe plate thickness, and wherein the first capacitive plate is separatedfrom the second capacitive plate by the separation distance.